Conventionally, diamond tools such as a cutting tool and a wear-resistant tool have been made using natural diamond or diamond produced by the high pressure high temperature method (HPHT). Natural diamond however exhibits large variations in quality, and cannot be supplied in a constant amount. The diamond produced by the high pressure high temperature method exhibits less variations in quality and can be supplied in a constant amount, but poses a problem that the cost for manufacturing facilities is high.
Another method of synthesizing diamond is a vapor phase synthesis method such as a chemical vapor deposition (CVD) method. For example, Japanese Patent Laying-Open No. 2005-162525 (hereinafter abbreviated as PTD 1) discloses diamond produced by the vapor phase synthesis method, which is transparent in an ultraviolet region and exhibits less crystal defects and strains. Furthermore, for example, Japanese Patent Laying-Open No. 2006-315942 (hereinafter abbreviated as PTD 2) discloses a diamond single crystal used in a semiconductor device substrate and exhibiting less strains. Furthermore, for example, Japanese Patent National Publication No. 2006-507204 (hereinafter abbreviated as PTD 3) discloses a CVD single crystal diamond material that is suitable to be used in an optical device or element.